(1) Field of the Invention
The invention relates to an arrangement for regenerating start-stop signals and dial pulses and converting the regenerated signals into an isochronous signal in which the start-stop signals are regenerated by means of a regeneration process having a sampling instants initiated by a stop-start transition and in which the dial pulses are regenerated by a combined regeneration process comprising two mutually exclusive regeneration processes which are initiable by the signal transitions in opposite directions and in which the signal samples taken at the sampling instants are stored in an elastic storage device (commonly referred to as a buffer memory) which is read at isochronous timing instants for forming an isochronous information signal.
The invention comes from the field of time-multiplex systems for telegraphy with bit interleaving, in particular such systems in which one element of the telegraph signal is represented by one bit in the isochronous signal.
The asynchronous regeneration process which is used in the multiplexer is based on sampling the successive elements of each character. This process is synchronized by the stop-start transition at the beginning of each character such that each element is sampled in its center.
The telex signals which are transmitted in accordance with the signalling system type B of the CCITT do not have the form of characters and render special measures necessary for their regeneration.
(2) Description of the Prior Art
German Auslegeschrift No. 2,321,469 (reference D 1) and the CCITT document Study Group IX-Contribution No. 12 of January 1974 (reference D 2) disclose a method for regenerating dial impulses.
This known method comprises:
a normal process with seven sampling instants which is initiated by the stop-start transition at the beginning of each series of dial pulses (10, 30, 50, 70, 90, 110, 130 ms)
a modified process with four sampling instants which is initiated by the start-stop transition which occurs at each following pulse of the same series (10, 30, 50, 70 ms)
In accordance with the CCITT recommendation U 2 (reference D3) the characteristics of the dial pulses may vary between the limits indicated here below:
rate: 9-11 pulses/sec.
pulse rate: TA/TZ=1.2-1.9
If dial pulses having these characteristics are regenerated in a manner indicated in references D1 and D2 and the regenerated signal is converted into an isochronous signal and the plurality of successive identical bits are taken into account (A: start polarity; Z: stop polarity), then the result is:
during a normal process:
2, 3, 4 or 5 bits A
1, 2 or 3 bits Z
during a modified process:
2, 3 or 4 bits A
2 or 3 bits Z.
The dial pulses are restituted from the isochronous signal at the receiving side. In accordance with reference D2 they must remain within the limits of CCITT recommendation U 24 (reference D4), that is to say:
TA: 44-98 ms (pulse duration)
TZ: 32-73 ms (pulse interval)
To this end reference D2 provides a prolongation to 50 ms of the intervals with polarity A which only comprise two bits A transmitted during a modified process.
In accordance with reference D2, however, it is not avoided that at the beginning of a series of dial pulses, intervals having the polarity A of 40 ms and 100 ms and an interval having the polarity Z of 20 ms may be produced.
In the CCITT recommendation R 101 (reference D 5) which relates to telegraph multiplexers of the present type the tolerances of reference D 4 are not taken over. In reference D 5 it is suggested to restitute the dial pulses within the narrower limits of reference D 3, that is to say:
TA: 49.6-72.8 ms
TZ: 31.4-50.5 ms